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    Sin 21 Degrees

    Sin, Cos, Tan, Cot of an Angle
    Function
    Angle (°)

    What is sin 21°?

    Answer

    sin 21° ≈
    0.3584

    Angle in radians: 21° = 7π/60. The point of the angle is in quadrant I, where sine is positive.

    ≈ — rounded to 4 decimal places. An exact form of sin 21° in square roots exists, but it is unwieldy — nested radicals.

    P(cos 21°, sin 21°) ≈ (0.9336, 0.3584)

    xyOP

    P(cos 21°, sin 21°) ≈ (0.9336, 0.3584)

    Highlighted: the projection on the y-axis — sine, y ≈ 0.3584.

    All four functions of 21°
    FunctionExact valueDecimal
    sin 21°—≈ 0.3584
    cos 21°—≈ 0.9336
    tan 21°—≈ 0.3839
    cot 21°—≈ 2.6051

    See Also

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    https://calculat.io/en/number/trigonometry/sin--21Copy
    <a href="https://calculat.io/en/number/trigonometry/sin--21">Sin 21 Degrees: Sine of 21° on the Unit Circle - Calculatio</a>Copy
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    Sin 21 Degrees: Sine of 21° on the Unit Circle. sin 21° ≈ 0.3584. The sine is the y-coordinate of the point at 21° on the unit circle.
    https://calculat.io/en/number/trigonometry/sin--21/generated.jpgCopy

    Sine of nearby angles

    Anglesin
    18°(√5 − 1)/4
    19°≈ 0.3256
    20°≈ 0.3420
    21°≈ 0.3584
    22°≈ 0.3746
    23°≈ 0.3907
    24°≈ 0.4067
    Recalculate with different values ↑

    FAQ

    What is sin 21°?

    sin 21° ≈ 0.3584

    Is there an exact value of sin 21°?

    Yes: 21° is a multiple of 3°, and the values of such angles can be written with square roots — but the expression is unwieldy, with nested radicals built from the values of 18° and 15° (3° = 18° − 15°). In practice the decimal is used: sin 21° ≈ 0.3584.

    Why does a calculator show 0.8367 for sin 21?

    The calculator is in radian mode (RAD): it takes sin 21 as the sine of 21 radians, sin 21 rad ≈ 0.8367. Switch it to degrees (DEG): sin 21° ≈ 0.3584. In radians the value is never undefined: π is irrational, so a whole number of radians never lands exactly on an axis.

    See Also